1. Field of the Invention
This invention relates to a scale for measuring the weight of an object. More particularly, it relates to a weight detecting apparatus as a means of enhancing the operation and performance of a device, by detecting the weight of an object and allowing the device to effectively utilize this weight information. For example, as a means that effectively utilizes the weight information, a heat cooking appliance is known, in which the cooking performance may be enhanced by detecting the weight of the food in the heating compartment and heating it at an optimum time and temperature for that weight. This invention relates to such a weight detecting apparatus.
2. Description of the Related Art
In a conventional scale, for example as shown in FIG. 1, the object to be measured is put on a tray 1, and its load is linked to a movable side spacer 3 by way of a load support 2. This spacer 3 is linked to a fixed side spacer 5 by way of leaf springs 4 vertically spaced in a parallel state. This second spacer 5 is fixed on a foundation 7 through a support 6. Two sheet metal electrodes 8 are respectively mounted on the movable side spacer 3 and the fixed side spacer 5.
When the object to be measured is put on the tray 1, the leaf springs 4 are deformed under its load, and the movable side spacer 3 side is displaced downward. As a result, the gap between the two sheet metal electrodes 8 changes, and the electrostatic capacity between the sheet metal electrodes varies. The weight is measured by detecting this change of electrostatic capacity.
However, in such a scale or weight detecting appratus of a cooking appliance, since the detection of weight depends on the electrostatic capacity between sheet metal electrodes, the following problems arise.
Firstly, the sheet metal electrodes 8 are exposed to the atmosphere, and dew or water drops may be formed between the sheet metal electrodes depending on the ambient humidity. Accordingly, the electrostatic capacity between the sheet metal electrodes varies, and the weight of the object cannot be detected accurately. Specifically, the cooking appliance is installed in a kitchen, and is exposed to steam generated from food, and the humidity varies significantly, making it difficult to detect the weight of the object accurately.
Secondly, when dust is deposited on the sheet metal electrodes 8 and absorbs moisture, the electrostatic capacity between the sheet metal electrodes varies, making it impossible to measure the weight of the object correctly.
Thirdly, the sheet metal electrodes have large dimensions, measuring in a range from about 50 mm by 50 mm to 100 mm by 100 mm, with the electrode gap ranging from 5 to 10 mm. Changes in the electrode gap caused by the load are about 2 to 3 mm, and in order to detect variations of electrostatic capacity, the electrodes are required to have a large area. Because the area of the electrodes is large and the dislocation between the electrodes is large, it is difficult to isolate the electrodes from fresh air to eliminate the effects of humidity. Thus, in the conventional device, since measures against the exposure of the electrodes to dust and humidity were difficult to take, it was extremely hard to detect the weight of the object accurately.